Hippopodina iririkiensis Tilbrook, 1999

Dick, Matthew H. & Grischenko, Andrei V., 2016, Rocky-intertidal cheilostome bryozoans from the vicinity of the Sesoko Biological Station, west-central Okinawa, Japan, Journal of Natural History 51, pp. 141-266 : 213-216

Hippopodina iririkiensis Tilbrook, 1999

( Figure 24 (c, d))

Hippopodina iririkiensis Tilbrook, 1999, p. 454 , fig. 2(a, c, e).

Hippopodina iririkiensis: Tilbrook et al. 2001, p. 90 , fig. 18(b). Tilbrook, 2006, p. 245. Dick et al. 2006, p. 2229, fig. 11(a).

Material examined

NSMT-Te 1141 (REEF-1), bleached, on SEM stub; NSMT-Te 1142, dried colony with ancestrular complex, REEF site; NSMT-Te 1143, seven dried specimens, REEF site; NSMT-Te 1144, five dried specimens, SES site.

Measurements

AzL, 0.82 – 1.03 (0.925 ± 0.071); AzW, 0.57 – 0.83 (0.711 ± 0.069) (n = 15, 1). OrL, 0.19 – 0.26 (0.229 ± 0.018); OrW, 0.19 – 0.24 (0.218 ± 0.014) (n = 15, 1). OvL, 0.57 – 0.70 (0.637 ± 0.044); OvW, 0.46 – 0.60 (0.534 ± 0.044) (n = 7, 1). Largest fragment observed, 30 × 13 mm.

Description

Colony forming a unilaminar, encrusting sheet, sometimes covering extensive areas; light tan in colour. Zooids ( Figure 24 (c)) large, distinct, delineated by a groove. Frontal wall convex, finely granulated, covered with numerous tiny, closely spaced pseudopores. Orifice keyhole shaped; short, wide poster separated from anter by conspicuous condyles; proximal margin concave. Orifice surrounded by low, raised rim. Primary orifice weakly dimorphic; generally wider in ovicelled (evident in zooids with developing ooecia) than in non-ovicelled zooids. Avicularia adventitious, lateral to the orifice; crossbar complete; mandible long-triangular; directed distomedially or sometimes distally; tip of rostrum not reaching zooidal midline. Avicularium lacking in most zooids, single in a few zooids; paired in only one among hundreds of zooids in several colonies. Ovicell ( Figure 24 (d)) hyperstomial, globose, longer than broad, closed by operculum; ooecium completely covered with small, closely spaced, infundibular pseudopores. Ancestrular complex (one observed) consists of triad of primary zooids.

Remarks

Avicularium frequency appears to vary among populations. Tilbrook (1999, p. 454) noted for specimens from Vanuatu, ‘ adventitious avicularia often paired, sometimes single or lacking ’. Dick et al. (2006) found the converse on Hawaii Island, where avicularia were usually single but sometimes paired. Among our specimens from Okinawa, most zooids lack an avicularium; when present, it is usually single.

Occurrence

Hippopodina iririkiensis was common at both the SES site, where it co-occurred with H. adunca , and the REEF site, where it did not ( Table 1). This species is widely distributed in the subtropical to tropical Indo-Pacific, with records from Mauritius, Indonesia, Australia, Indonesia, the Philippines and Vanuatu ( Tilbrook 1999; Tilbrook et al. 2001); the Solomon Islands ( Tilbrook 2006); and Hawaii ( Dick et al. 2006). It also appears to occur in the Mediterranean ( Tilbrook 1999), where it may have been introduced from the Red Sea through the Suez Canal.

Genus Thornelya Harmer, 1957

Thornelya fuscina Tilbrook, Hayward, and Gordon, 2001

( Figure 25 (a))

Thornelya fuscina Tilbrook, Hayward, and Gordon, 2001, p. 90 , fig.17(e, f).

Thornelya fuscina: Tilbrook 2006, p. 249 , pl. 54E, F.

Material examined

NSMT-Te 1145 ( SES- 11), bleached, on SEM stub.

Measurements

AzL, 0.42 – 0.64 (0.534 ± 0.077); AzW, 0.28 – 0.48 (0.388 ± 0.060) (n = 12, 1). OrL, 0.15 – 0.17 (0.162 ± 0.004); OrW, 0.13 – 0.14 (0.129 ± 0.004) (n = 12, 1).

Description

Colony forming a unilaminar, encrusting sheet; our specimen small, comprising about 40 zooids. Zooids distinct; frontal wall convex, tumid; weakly rugose, covered by numerous circular, sometimes infundibular pseudopores, except in raised zone around orifice; around eight usually slit-like but sometimes round areolae along each lateral margin. Primary orifice not immersed; longer than broad; condyles conspicuous, rounded, directed proximomedially; poster broadly concave. Marginal zooids have two (39%), three (54%) or four (7%) small, ephemeral tubular distal spines (n = 28). Avicularia adventitious; small, paired, in distolateral corners of zooid, lateral to orifice; chamber raised, bearing small pseudopore at proximal end. Rostrum raised distally; mandible longtriangular, acute, directed distomedially or sometimes medially; crossbar complete. No complete ovicells observed. Ancestrula not observed.

Remarks

This species has small, usually paired lateral-oral avicularia and relatively few oral spines. According to other descriptions, the ovicell is hyperstomial; the ooecium is globose, slightly broader than long, similar in texture to the frontal wall, with small pseudopores over the entire surface, and closed by the maternal operculum. Type material from Vanuatu ( Tilbrook et al. 2001) differs from our specimen in having three or four rather than two to four oral spines, and some zooids have a third, median avicularium associated with the orifice, which we did not observe . Some zooids in specimens from the Solomon Islands have one of the lateral-oral avicularia markedly larger than the other ( Tilbrook 2006), which we also did not observe. For a discussion of differences among species in Thornelya , see Remarks for T. perarmata below.

Occurrence

We found a single colony at the SES site. Thornelya fuscina is widely distributed in the subtropical to tropical Indo-West Pacific, previously reported from Sri Lanka, New Guinea (32 m), Tuvalu (146 m) and Vanuatu ( Tilbrook et al. 2001), and from the Solomon Islands ( Tilbrook 2006).

Figures

Figure 24. (a, b) Hippopodina adunca Tilbrook, NSMT-Te 1137: (a), view of colony; note small relative size of zooids in overgrowing Puellina harmeri colony at upper right; (b) ovicelled and non-ovicelled autozooids; note unusual presence of avicularium on ovicelled zooids. (c, d) Hippopodina iririkiensis Tilbrook, NSMT-Te 1141: (c) view of colony; (d) ovicelled and non-ovicelled autozooids. All panels are scanning electron microscopic images of bleached specimens. Scale bars: a, c = 1.0 mm; b, d = 500 µm.

Figure 25. (a) Thornelya fuscina Tilbrook, Hayward, and Gordon, NSMT-Te 1145: autozooids. (b) Thornelya perarmata Harmer, NSMT-Te 1146: autozooids; arrows and arrowheads indicate two types of adventitious avicularia (see the text). (c, d) Gigantopora pupa (Jullien), NSMT-Te 1147: (c) colony view, showing ovicelled and non-ovicelled autozooids (arrowhead, minute oral spine); (d) orifice. All panels are scanning electron microscopic images of bleached specimens. Scale bars: a, b = 300 µm; c = 1.0 mm; d = 200 µm.